Landing an aircraft is the most demanding task in flying. During the landing process, the aircraft must transition from operating in three dimensions of motion to operating in only two dimensions and must be brought to a safe and complete stop. To perform the landing properly, the aircraft must approach the runway within certain attitude, track, speed and rate of descent limits. An approach outside of these limits can result in the aircraft making a “hard” landing, overrunning the runway end, or otherwise contacting the runway surface in an uncontrolled manner. Any one of these events has the potential to cause severe damage to the aircraft and may additionally result in passenger injuries or fatalities.
Factors which contribute to unstable approaches include: wind conditions that alter the speed and path of the aircraft, excessive speed and/or variations in the speed flown during the approach; failure to maintain a glide path that intersects the runway at the touchdown point; failure to track the center line of the runway; and equipment malfunctions. Pilots are trained to monitor these conditions during the approach and to initiate a go-around maneuver if the approach is unstabilized and a safe landing is not assured. The effectiveness of pilot training as a preventive measure ultimately depends, however, on the skill and judgment of the pilot in recognizing the unstabilized approach condition and executing the appropriate response as taught. Pilots with varying levels of skill are likely to respond differently to the same scenario.
In addition, unstabilized approaches are not the sole cause of runway overruns. A contaminated runway surface can reduce the braking effectiveness of the aircraft and increase the aircraft stopping distance. Thus, even with a stabilized approach, the aircraft may still be in danger of overrunning the runway end in some circumstances. The most common runway contaminates are rainwater and snow.
Automatic landing systems that guide the aircraft to touchdown do not completely solve the problems identified above. The control laws that govern operation of such systems may not always be able to reject disturbances such as those due to wind gusts, or certain equipment malfunctions. In such circumstances, the aircraft may still wind up on a destabilized approach and/or the automatic landing system must be disengaged. The pilot must still monitor and anticipate the need for a go-around even when such systems are in use. Landing systems also work best when precision approach guidance is available to the intended runway. Precision approaches provide both horizontal and vertical guidance on approach. Not all runways have precision approaches.
Therefore, there exists a need for providing pilots with information regarding an unstable approach to landing.